1. Field of the Invention
The present invention relates generally to improvements in the electrical current transfer device for transferring electrical current between relatively rotatable members, the broad class of such devices generally being referred to as slip rings. Specifically, the invention relates to an improved current transfer device for conducting heavy currents between stator and rotor members, such as between the relatively rotatable members of a solar panel pointing device utilized in aerospace applications, or for conducting power supply currents between spun and despun sections of a spin stabilized satellite, while having relatively low friction torque from the current transfer device.
2. Description of the Prior Art
Rolling electrical conductor assemblies are not broadly new and have heretofore been proposed for use in place of the more conventional slip ring and brush assemblies. For example, U.S. Pat. No. 4,098,546, issued to the Applicant's assignee, discloses a full rotational freedom, substantially zero friction electrical conductor assembly for conducting electrical currents between relatively rotatable members of sensitive instruments such as gyroscopic devices and the like. Each electrical transfer unit of the assembly comprises a pair of coaxial, concentric, coplanar continuous, concave conductor rings, one mounted on a relatively fixed member and the other mounted on a rotatable member, the relative diameters of the rings providing a substantial annular radial gap therebetween. A resilient electrically conducting continuous filamentary loop is disposed in the radial gap such that its generally flat outside surface contacts and rolls on the concave surface of the conductor rings. The loop or conductor interface provides self-capturing and retaining forces to accommodate any misalignment between the rings and movements of the loops within the radial gap in a vibratory environment, all without producing frictional torques on the rotatable member.
In high power applications a major disadvantage of the above described apparatus is that all the electric current to be conducted from one ring to the other must pass through only a single conductor loop. Clearly the current carrying capacity of that assembly is limited to that of the conductor loop whose cross section dimensions are constrained to satisfy the physical requirements of the rolling ring contact principles. Although one could simply add more conductive loops evenly spaced from one another in the radial gap to increase the current carrying capacity and in theory they would maintain their spaced relationship, in practice, however, mechanical perfection is not possible and tolerances exist which cause the rings eventually to contact one another causing friction and thereby defeating the basic advantage of roll ring contacts as taught in the patent number 4,098,546. Thus there is a need to provide industry, such as the aerospace industry, with a solution to the problem of transferring relatively high electrical current between stator and rotor members while utilizing the substantially zero friction roll ring technology. The present invention provides a roll ring contact assembly which retains the substantially zero friction advantage yet allows very high currents to be conducted between the stator and rotor of the device.